Allow atoms in io* funs

Take integers or atoms in ioc, iow, iorw, to allow lookup of values
based on platform.

From dialyzer:

bpf.erl:120: The call bpf:ior(66,'gseesent',4) will never return since it differs in the 2nd argument from the success typing arguments: (integer(),integer(),integer())
bpf.erl:181: The call bpf:iow(66,'sseesent',4) will never return since it differs in the 2nd argument from the success typing arguments: (integer(),integer(),integer())